Appliance of Science: what happens when it feels like you're falling as you fall asleep

You’ve had a long day, you finally get to bed and just as you drift off to sleep… bam! You experience a shock sensation like you are falling in mid-air and it is enough to jolt you back awake again. Sound familiar? It probably does, as at least seventy percent of us experience this sensation at some stage, but why do we feel like we are falling as we fall asleep?

What a jerk